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recommendations for distributing DMX though-out an auditorium

Discussion in 'Lighting and Electrics' started by Jayme McColgan, Jul 29, 2018.

  1. Jayme McColgan

    Jayme McColgan Member

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    I'm looking to add some more dmx connections in the existing rig of a church. I want to add enough to plan for the future. whats the best way to do this? are artnet nodes the best way? or just running a ton of dmx cable?
     
  2. Colin Bishop

    Colin Bishop ValleyPoint Church AVL Tech Premium Member

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    Depends on what the existing infrastructure is. You can buy a centralized art net node and run DMX cable out of that to the fixtures or you can go the distributed route with a network switch and nodes spread out near your lighting positions. In my church we have a Chauvet Net-X connected via art net to our console and then DMX (ran over cat5) to our lighting positions. Works great for us.
     
    Last edited: Jul 29, 2018
  3. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    Not sure any one way is best. My current approach is network to lighting positions and ETC gatweways - mostly 4 port - and portable DMX from there.

    If I'm distributing DMX from a central location or two, I rack up 4 port nodes and distribute using category wiring, not splitters.

    And then theres wireless.....

    Most of my wiring is done by union or prevailing wage electricians so install cost is important. Installing yourself may be different.

    Also looking ahead and sering if more exoanion in a few years is likely.
     
  4. Jayme McColgan

    Jayme McColgan Member

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    yeah, we have a Proplex artnet box and some cat5 running to FOH. I'm looking to run dmx into the rig for our fixtures. ideally, I would like to have access to 4 different universes in 6-8 areas.
     
  5. SteveB

    SteveB Well-Known Member

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    Maybe a Pathway Connectivity Octo ?. Can do 8 DMX outputs on any universes, talks ArtNet.

    Or do you want an entire Ethernet network laid out thru the entire space for future proofing ?.

    EDIT: As per Bill's following comment, the Octo requires local power and does not use PoE.
     
    Last edited: Jul 30, 2018
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  6. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    The only thing I'd say about the selecting nodes, especially if distributed, think about wall warts vs. POE. It might or might not make a difference for install.
     
  7. Rob

    Rob Active Member

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    For permanently installed applications we (Pathway) would suggest:
    This will give you the most extensible and flexible system (multiple protocols, sACN priorities, sub-universe patching, precedence, crossfading between sources, RDM) at the lowest per-port cost.
     
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  8. Jayme McColgan

    Jayme McColgan Member

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    I'm not super worried about power. there are lots of places to get power where I want to drop these nodes.
     
  9. RickR

    RickR Well-Known Member

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    When I started doing network systems I put a gateway at each location. I've seen many like that by others.

    Now I do centralized gateways. Wire and labor costs are similar because category cable is feally cheap. Gear costs are lower and maintenance is easier.
     
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  10. Stephen Ellison

    Stephen Ellison Member

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    First plan to use Cat5 for the permanent cable runs, this allows for expansion of the system down the road. Depending on your console the best answer is to start with a network connection out of the console so you can get multiple universe's on one cable. You run this to a rack where you start setting up a distribution point. From the distribution point you can use a network switch, go with a pro grade with POE. Run from the distribution point to locations near your lighting positions and don't forget stage level. Here is where you switch from network to DMX with nodes. Since you want multiple universes this is the easiest way to get them spread out. Once you switch to DMX you still may need opto-splitters if any run will get near the 32 load limit. For anyone else if you can't jump past two universes still put in the CAT5 because you can have opto-splitters at the first distribution point and then later when you need more channels you can switch the dumb output jack for a single port node which fits in the same single gang box. That is why the switch wants to have POE.

    If anyone is going to LDI I will be teaching a class there on this very subject.
     
  11. teqniqal

    teqniqal Well-Known Member

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    If you distribute a DMX signal, it should either be over cable specifically designed to carry RS485, (i.e. 120 Ohm nominal impedance), or it should be shielded CAT cable (CAT5 is OK, but you can always 'hedge your bet' and go with CAT6A to further 'future-proof' the installation). The CAT cable nominal impedance is very close to the EIA RS485 spec and is generally approved for DMX. The only difficulty is physically terminating the CAT type cable into the back of the XLR connectors - it can be a bit fragile so handling it carefully as you stuff it in the back-box is important.

    If budget is an issue, also to be considered is the use of DMX buffered receptacles like those made by Doug Fleenor Designs or Goddard Designs. These are essentially a 'private' DMX buss that connect all the receptacles together that the end-user does not connect directly to, so each outlet can have up to 31 devices attached. The nice thing about this is if the student screws-up and shorts the DMX line, the whole system doesn't fail, just the one line they have connected to. You will need to provide a separate pair of wires to power the buffered outlets. They run off of 24 VDC, so depending upon how many buffered receptacle plates and how long the run is from the power supply, you can calculate the optimal size wire to deliver the power without excessive voltage sag (IxR loss in the wire). The advantage to this system is that you run a single pair of data and power cables out to a series of up to 31 receptacles. This can save substantially with respect to having to home-run each DMX or Data cable from each receptacle back to a DMX opto-splitter or a Data Switch (if network based). If you are installing this in conduit (highly recommended to protect the cabling) then the conduit can be significantly smaller (about 1/2" to 3/4" EMT), whereas if you have twenty outlets that each must be home-run the conduit size can increase significantly. The Goddard Designs device will pass RDM, too (not sure about the DFD device).

    You can make a hybrid system, too: run a network line and DC power out to a data-to-DMX Node at an electric batten or catwalk, then install a dozen or more buffered DMX receptacles along the batten or catwalk. This lets you assign the universe separately to each electric batten and catwalk. (This could also be done by using a high quality DMX opto-splitter that has a network input.)

    The trade-off as to how many 512 channel universes you may need at a given location should be considered. More and more lighting devices chew-up 30-100 DMX channels, so 512 channels may not go as far as it used-to, particularly if you are using the devices in 16 bit mode. This is why installing cable that home-runs all the way back to a switch location becomes necessary for more complex locations. More wire = larger and/or more conduits. Conduit is worth every penny when it comes to efficiently pulling cables through a building and protecting cabling from damage in the rough-and-tumble world of stage production. When you leave cables exposed for stuff to snag upon - stuff will snag upon it -- guaranteed.
     
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  12. Stephen Ellison

    Stephen Ellison Member

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    I would add that DMX over CAT wire was accepted into the standard after testing. You can connect up to 32 devices off a regenerated DMX split, although alot of tech's limit the number of devices below that to insure integrity or in the case of long cable runs.
     
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  13. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    Just a note on at least ETC nodes. Im pretty sure each dmx port is limited to 32 devices. You cant sling a splitter or buffered ports on it and add more devices. Just a caution on Erich's hybrid approach.
     
  14. DavidJones

    DavidJones Active Member

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    How can it tell how many devices are attached to it? There is no return signal coming from the fixtures if they do not have RDM. I suppose it could be measuring voltage drop or current draw, but this seems like it would vary quite a bit with different cables and fixture combinations.
     
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  15. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    I don't know. I was told this by an etc rep. Maybe they were wrong but usually a very reliable source. Perhaps one of the etc folks who post here will answer your question.
     
  16. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    @BillConnerFASTC there might be some context or caveats missing from that limit from the ETC rep.

    For DMX, the limit is 32 unit loads which may be much more than 32 devices depending on the device and the cabling, as has been discussed many many times before. An ETC node is fully compliant in that regard and fully supports splitters or any other DMX device with no practical limit on the total quantity downstream of the gateway.

    Where things get complex is with RDM merging. There are limits to the number of RDM devices that can respond via the gateway since the gateway has to queue up the RDM responses from all the downstream devices and serialize them for the upstream controller. The internal buffer is finite, as is the patience of any controller waiting to receive the RDM data from all the devices.
     
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  17. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    I'll assume you are correct. Have you actually tested it?
     
  18. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    I have not tested it however there is no engineering reason that any node made by any manufacturer would have any limitations on the number of downstream devices, assuming it is properly connected and stays within the load limits for the transmitter. For DMX, all any node does is receive an Ethernet packet and transmit it as a DMX bit string. It has no way to know how many devices are receiving that bit string, nor how many of those devices might be re-transmitting it to yet more devices.
     
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  19. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    From ETC: "The actual limit is 128 devices per gateway, which of course on a four port comes out to 32 devices per port (but you could have e.g. 64 devices on port 1 and 64 on port 2, none on 3/4 and that would be OK)."

    It is the RDM memory and the RS485 unit load, which I believe most manufacturers do not publish.

    So plan for more and if it doesn't work, reduce the number of devices.

    For me, laying out a new install, planning for more than the 32/line or 128/node would simply be negligent. It does not seem like the number of DMX devices will become fewer in the future, nor that the number of required addresses will get smaller.

    On a single batten auditorium or stage width batten/position (typically 4 over stage and 3 foh in my projects), how much DMX is good planning? I've been trying for at least a universe per batten/position capability, and in some cases a second network tap for expected expansion. I also try to keep in mind cost. Another network tap/another universe is practically nothing in the context of a system with 2-3 Sensor IQ's, a Paradigm system, an Ion, 100-150 LED fixtures, two Robert Juliat follow spots, distro, network, accessories, etc. And its harder to get infrastructure upgrades compared to a couple of instruments, and it costs a lot more after initial construction.

    Just a note on the choice of 4 port nodes. While I use singles and duals, the cost per DMX port is enough lower with 4 ports that I try to use as many of them as possible.
     
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  20. sk8rsdad

    sk8rsdad Well-Known Member Premium Member Fight Leukemia

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    Full respect for future-proofing a facility and using conservative estimates.

    DMX isn't going away any time soon. However, these days I would be designing for 2 or more POE ethernet drops per batten (redundancy), and installing nodes directly on the batten as required with as many ports as necessary. Run the copper but maybe not terminate everything to save some money. The ethernet drop can also be used for sACN, Art-Net, Dante, Crestron, IP cameras, or whatever else might find it's way to the rig. Some fixtures, Clay Paky comes to mind, will act as Art-Net nodes for other DMX devices downstream.
     
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